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KVM: arm/arm64: Correct CPSR on exception entry

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When KVM injects an exception into a guest, it generates the CPSR value
from scratch, configuring CPSR.{M,A,I,T,E}, and setting all other
bits to zero.

This isn't correct, as the architecture specifies that some CPSR bits
are (conditionally) cleared or set upon an exception, and others are
unchanged from the original context.

This patch adds logic to match the architectural behaviour. To make this
simple to follow/audit/extend, documentation references are provided,
and bits are configured in order of their layout in SPSR_EL2. This
layout can be seen in the diagram on ARM DDI 0487E.a page C5-426.

Note that this code is used by both arm and arm64, and is intended to
fuction with the SPSR_EL2 and SPSR_HYP layouts.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200108134324.46500-3-mark.rutland@arm.com
This commit is contained in:
Mark Rutland 2020-01-08 13:43:23 +00:00 committed by Marc Zyngier
parent a425372e73
commit 3c2483f154
3 changed files with 114 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
arch/arm/include/asm/kvm_emulate.h
View File

@ -14,13 +14,25 @@
#include <asm/cputype.h>
/* arm64 compatibility macros */
#define PSR_AA32_MODE_FIQ FIQ_MODE
#define PSR_AA32_MODE_SVC SVC_MODE
#define PSR_AA32_MODE_ABT ABT_MODE
#define PSR_AA32_MODE_UND UND_MODE
#define PSR_AA32_T_BIT PSR_T_BIT
#define PSR_AA32_F_BIT PSR_F_BIT
#define PSR_AA32_I_BIT PSR_I_BIT
#define PSR_AA32_A_BIT PSR_A_BIT
#define PSR_AA32_E_BIT PSR_E_BIT
#define PSR_AA32_IT_MASK PSR_IT_MASK
#define PSR_AA32_GE_MASK 0x000f0000
#define PSR_AA32_DIT_BIT 0x00200000
#define PSR_AA32_PAN_BIT 0x00400000
#define PSR_AA32_SSBS_BIT 0x00800000
#define PSR_AA32_Q_BIT PSR_Q_BIT
#define PSR_AA32_V_BIT PSR_V_BIT
#define PSR_AA32_C_BIT PSR_C_BIT
#define PSR_AA32_Z_BIT PSR_Z_BIT
#define PSR_AA32_N_BIT PSR_N_BIT
unsigned long *vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num);

1
arch/arm64/include/asm/ptrace.h
View File

@ -62,6 +62,7 @@
#define PSR_AA32_I_BIT 0x00000080
#define PSR_AA32_A_BIT 0x00000100
#define PSR_AA32_E_BIT 0x00000200
#define PSR_AA32_PAN_BIT 0x00400000
#define PSR_AA32_SSBS_BIT 0x00800000
#define PSR_AA32_DIT_BIT 0x01000000
#define PSR_AA32_Q_BIT 0x08000000

111
virt/kvm/arm/aarch32.c
View File

@ -10,6 +10,7 @@
* Author: Christoffer Dall <c.dall@virtualopensystems.com>
*/
#include <linux/bits.h>
#include <linux/kvm_host.h>
#include <asm/kvm_emulate.h>
#include <asm/kvm_hyp.h>
@ -28,22 +29,112 @@ static const u8 return_offsets[8][2] = {
[7] = { 4, 4 }, /* FIQ, unused */
};
/*
* When an exception is taken, most CPSR fields are left unchanged in the
* handler. However, some are explicitly overridden (e.g. M[4:0]).
*
* The SPSR/SPSR_ELx layouts differ, and the below is intended to work with
* either format. Note: SPSR.J bit doesn't exist in SPSR_ELx, but this bit was
* obsoleted by the ARMv7 virtualization extensions and is RES0.
*
* For the SPSR layout seen from AArch32, see:
* - ARM DDI 0406C.d, page B1-1148
* - ARM DDI 0487E.a, page G8-6264
*
* For the SPSR_ELx layout for AArch32 seen from AArch64, see:
* - ARM DDI 0487E.a, page C5-426
*
* Here we manipulate the fields in order of the AArch32 SPSR_ELx layout, from
* MSB to LSB.
*/
static unsigned long get_except32_cpsr(struct kvm_vcpu *vcpu, u32 mode)
{
u32 sctlr = vcpu_cp15(vcpu, c1_SCTLR);
unsigned long old, new;
old = *vcpu_cpsr(vcpu);
new = 0;
new |= (old & PSR_AA32_N_BIT);
new |= (old & PSR_AA32_Z_BIT);
new |= (old & PSR_AA32_C_BIT);
new |= (old & PSR_AA32_V_BIT);
new |= (old & PSR_AA32_Q_BIT);
// CPSR.IT[7:0] are set to zero upon any exception
// See ARM DDI 0487E.a, section G1.12.3
// See ARM DDI 0406C.d, section B1.8.3
new |= (old & PSR_AA32_DIT_BIT);
// CPSR.SSBS is set to SCTLR.DSSBS upon any exception
// See ARM DDI 0487E.a, page G8-6244
if (sctlr & BIT(31))
new |= PSR_AA32_SSBS_BIT;
// CPSR.PAN is unchanged unless SCTLR.SPAN == 0b0
// SCTLR.SPAN is RES1 when ARMv8.1-PAN is not implemented
// See ARM DDI 0487E.a, page G8-6246
new |= (old & PSR_AA32_PAN_BIT);
if (!(sctlr & BIT(23)))
new |= PSR_AA32_PAN_BIT;
// SS does not exist in AArch32, so ignore
// CPSR.IL is set to zero upon any exception
// See ARM DDI 0487E.a, page G1-5527
new |= (old & PSR_AA32_GE_MASK);
// CPSR.IT[7:0] are set to zero upon any exception
// See prior comment above
// CPSR.E is set to SCTLR.EE upon any exception
// See ARM DDI 0487E.a, page G8-6245
// See ARM DDI 0406C.d, page B4-1701
if (sctlr & BIT(25))
new |= PSR_AA32_E_BIT;
// CPSR.A is unchanged upon an exception to Undefined, Supervisor
// CPSR.A is set upon an exception to other modes
// See ARM DDI 0487E.a, pages G1-5515 to G1-5516
// See ARM DDI 0406C.d, page B1-1182
new |= (old & PSR_AA32_A_BIT);
if (mode != PSR_AA32_MODE_UND && mode != PSR_AA32_MODE_SVC)
new |= PSR_AA32_A_BIT;
// CPSR.I is set upon any exception
// See ARM DDI 0487E.a, pages G1-5515 to G1-5516
// See ARM DDI 0406C.d, page B1-1182
new |= PSR_AA32_I_BIT;
// CPSR.F is set upon an exception to FIQ
// CPSR.F is unchanged upon an exception to other modes
// See ARM DDI 0487E.a, pages G1-5515 to G1-5516
// See ARM DDI 0406C.d, page B1-1182
new |= (old & PSR_AA32_F_BIT);
if (mode == PSR_AA32_MODE_FIQ)
new |= PSR_AA32_F_BIT;
// CPSR.T is set to SCTLR.TE upon any exception
// See ARM DDI 0487E.a, page G8-5514
// See ARM DDI 0406C.d, page B1-1181
if (sctlr & BIT(30))
new |= PSR_AA32_T_BIT;
new |= mode;
return new;
}
static void prepare_fault32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset)
{
unsigned long cpsr;
unsigned long new_spsr_value = *vcpu_cpsr(vcpu);
bool is_thumb = (new_spsr_value & PSR_AA32_T_BIT);
u32 return_offset = return_offsets[vect_offset >> 2][is_thumb];
u32 sctlr = vcpu_cp15(vcpu, c1_SCTLR);
cpsr = mode | PSR_AA32_I_BIT;
if (sctlr & (1 << 30))
cpsr |= PSR_AA32_T_BIT;
if (sctlr & (1 << 25))
cpsr |= PSR_AA32_E_BIT;
*vcpu_cpsr(vcpu) = cpsr;
*vcpu_cpsr(vcpu) = get_except32_cpsr(vcpu, mode);
/* Note: These now point to the banked copies */
vcpu_write_spsr(vcpu, new_spsr_value);
@ -84,7 +175,7 @@ static void inject_abt32(struct kvm_vcpu *vcpu, bool is_pabt,
fsr = &vcpu_cp15(vcpu, c5_DFSR);
}
prepare_fault32(vcpu, PSR_AA32_MODE_ABT | PSR_AA32_A_BIT, vect_offset);
prepare_fault32(vcpu, PSR_AA32_MODE_ABT, vect_offset);
*far = addr;